HMMWV Overheat Q's and pictures

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hooneybee

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Did you check if your radiator is painted black?
I have just purchased m998 and it was overheating and realized the builder painted the truck without blocking out the radiator. I’ve spent 3 days stripping the paint and it runs a lot cooler.
Lol.

I fixed the trans leak and everything is going swimmingly so I drive it at least weekly. I usually travel about 100+ miles and the temp still registers the same and doesn't boil over or anything. I blew a hose (hose clamp failed) last year and got to see what everheating looks like...the needle pegged right and I put off a spy hunter like smoke screen. BTW you don't realize how much antifreeze is in a hmmwv until you blow a hose and turn it all into smoke and make everyone in indianapolis smell like maple pancakes. Once you fix the hose you'll need to take out a loan to refill it. I haven't swapped the temp sender or gauge yet but I assume everything is fine, just registering high.
 

David172

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My 1991 6.2 had been running fine, temp rising to 220, fan kicking on cooling the truck back down to 200. It worked liked this for the last two years with no issues. The fan stopped engaging and the temp quickly rose to 240. I was able to stop and did not overheat it. I was glad to find this post thread and replaced the thermostatic switch as instructed with what was pictured as the exact part number. Now my cooling fan engages at 180 degrees and stays on continually. The truck never goes over 200 degrees, but the cooling fan never disengages. Is my thermostat stuck? Is the thermostatic control switch bad? I am not super mechanical and don't know where to turn next. Any help would be appreciated. Thanks
 

Retiredwarhorses

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My 1991 6.2 had been running fine, temp rising to 220, fan kicking on cooling the truck back down to 200. It worked liked this for the last two years with no issues. The fan stopped engaging and the temp quickly rose to 240. I was able to stop and did not overheat it. I was glad to find this post thread and replaced the thermostatic switch as instructed with what was pictured as the exact part number. Now my cooling fan engages at 180 degrees and stays on continually. The truck never goes over 200 degrees, but the cooling fan never disengages. Is my thermostat stuck? Is the thermostatic control switch bad? I am not super mechanical and don't know where to turn next. Any help would be appreciated. Thanks

You bought a chinese knock off from eBay? Those are set to open at the wrong temp.
order from HPG or Kascar and get the correct OEM switch.
 

David172

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Thanks so much for your response. That is what I suspected. I tried to buy OEM from Midwest Military Equipment, but what I received did not look like the OEM shown on their website or the part on my H1. It did look like a ebay knock-off. I called them today and they are sending me a replacement at no charge. He did tell me my product had shipped from one of their distributors and not from their home location but was supposed to have been OEM. The call went very well and I am hopeful this will solve the problem. Thanks for giving me the info and confidence to question the part. I will re-post when this is resolved. Thanks
 

Retiredwarhorses

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Stick with buying from Kascar, HPG or MAC Motor’s...that is unless you know what to look for.
I call BS on the “it shipped from somewhere else”
 

86humv

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Thanks so much for your response. That is what I suspected. I tried to buy OEM from Midwest Military Equipment, but what I received did not look like the OEM shown on their website or the part on my H1. It did look like a ebay knock-off. I called them today and they are sending me a replacement at no charge. He did tell me my product had shipped from one of their distributors and not from their home location but was supposed to have been OEM. The call went very well and I am hopeful this will solve the problem. Thanks for giving me the info and confidence to question the part. I will re-post when this is resolved. Thanks
If they send another bad one...I have some OEM ones.
 

G3isMe

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I am having similar high temp issues with my 2003 M1045 A2 Slant Back. I just took possession of the vehicle about 3 weeks ago from GovPlanet and have only driven it about 20 miles. The engine temp goes up to about 240 F within 5 minutes of driving. I am in Texas south of Houston and the air temps are around 95+ so I am sure that adds to it. I have a 1992 M998 and it runs at about 210 F even in this horrendous heat. My plan is to start with a coolant drain and flush and the installation of a new thermostat. I looked at Kascars and they have about 10 different thermostats. Does anyone have a part number for the stock thermostat? Are the thermostats for a 6.2 and a 6.5 interchangeable? I want to avoid a Chinese knockoff so I am trying to avoid the local auto parts store unless it is the last resort. That being said, will any thermostat for a GM 6.5L diesel work? My engine is a Melton. Thanks in advance.
 
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Retiredwarhorses

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I am having similar high temp issues with my 2003 M1045 A2 Slant Back. I just took possession of the vehicle about 3 weeks ago from GovPlanet and have only driven it about 20 miles. The engine temp goes up to about 240 F within 5 minutes of driving. I am in Texas south of Houston and the air temps are around 95+ so I am sure that adds to it. I have a 1992 M998 and it runs at about 210 F even in this horrendous heat. My plan is to start with a coolant drain and flush and the installation of a new thermostat. I looked at Kascars and they have about 10 different thermostats. Does anyone have a part number for the stock thermostat? Are the thermostats for a 6.2 and a 6.5 interchangeable? I want to avoid a Chinese knockoff so I am trying to avoid the local auto parts store unless it is the last resort. That being said, will any thermostat for a GM 6.5L diesel work? My engine is a Melson rebuild. Thanks in advance.
Is your fan clutch engaging? Very common for most of these m1045’s and m1123’s to have frozen and inop fan clutch’s from sitting for 9hrs in the desert. Have you unplugged your TDM to see if it engages and defaults to locked on?
These A2’s run at 220 all day long...only had one or 2 that ran at less then that, but this is operating temp.
 

G3isMe

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Is your fan clutch engaging? Very common for most of these m1045’s and m1123’s to have frozen and inop fan clutch’s from sitting for 9hrs in the desert. Have you unplugged your TDM to see if it engages and defaults to locked on?
These A2’s run at 220 all day long...only had one or 2 that ran at less then that, but this is operating temp.
The fan does come on so that is working. It makes me feel better to hear that 220 is normal. I thought when it reached that temp it was on the way to overheating. If the fan is engaging can one assume that the TDM is operating correctly? Thanks again for the education, it is much appreciated.
 

G3isMe

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Today I drove mine about 10 miles and this is the gauge reading, pretty close to 240 F with an ambient air temperature of over 100 this afternoon. I lifted the hood when I got home and the fan was running. After reading the similar overheating thread and reading the cooling troubleshooting section of Tech Memo "TM 9-2320-280-20-1", the trouble shooting methods make much more sense to me know. I am going to try disconnecting the TDM as per Retiredwarhorses advice and blowing air into the fan clutch line as I now think my fan is spinning but not engaging.
 

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Andyrv6av8r

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I am having similar high temp issues with my 2003 M1045 A2 Slant Back. I just took possession of the vehicle about 3 weeks ago from GovPlanet and have only driven it about 20 miles. The engine temp goes up to about 240 F within 5 minutes of driving. I am in Texas south of Houston and the air temps are around 95+ so I am sure that adds to it. I have a 1992 M998 and it runs at about 210 F even in this horrendous heat. My plan is to start with a coolant drain and flush and the installation of a new thermostat. I looked at Kascars and they have about 10 different thermostats. Does anyone have a part number for the stock thermostat? Are the thermostats for a 6.2 and a 6.5 interchangeable? I want to avoid a Chinese knockoff so I am trying to avoid the local auto parts store unless it is the last resort. That being said, will any thermostat for a GM 6.5L diesel work? My engine is a Melson rebuild. Thanks in advance.
My 1045A2 runs up to 210, fan kicks in and runs until back down to 190. On 90 degree days it takes around 5 minutes to repeat.
 

G3isMe

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Today I unplugged my TDM and the fan did engage. It didn't appear to move a full 1/4" but it did move forward. While it did engage it didn't sound like it had any effect on engine speed nor did it blow off my hat. I've read others here state that that you need to hold your cover when it engages. While I know they are being somewhat facetious that certainly wasn't even close to the case with mine....:???:
 
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Milcommoguy

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Rev it up a bit. At idle doing the unplug test, it should be easy to see clutch lock up movement. Should hear the fan producing air flow. Rev it up for the big leaf blower action. At cruising speeds (50 or so) when that fan kicks in, you will KNOW it. If not, something still not quite right.)

I have notice (and others observations may differ) If the fan is continually engaged (as in stuck / locked-up) AND cooling system is in good order (radiator stack not clogged with leaves or nests, radiator radiating and holding pressure, pump a pumping, fan a fanning, thermostat opening, and going down the road it would be hard to hit 195-200 degrees. Winter time it take forever to warm up for the thermostat to completely open.

109 degrees in the Mojave Desert today. Fan cycles on for a minute, off for for three. Temperature gauge up 230 and down 190 following fan cycling. It's a HUMMWV thing. Scares the Jeeper guys right off the trail.

That's how it is & hot as heck, CAMO
 
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G3isMe

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Haha, no, definitely not seeing nor hearing the leaf blower effect. I assume that my next step is to determine if the fan engages when the engine is hot, e.g., over 220 F. If it isn't engaged but does if I unplug the TDM, the TDM is faulty. If it is engaged when hot, the next option is replace thermostat?
 

Milcommoguy

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Check the thermal switch in the crossover. It applies power to the TDM and on to the Cadillac valve. Sounds like the switch might ?? not be opening to de-energize the TDM and on to the valve. Yes, it works backward from what one might think. Maybe stuck in the closed position (the juice is ON) or wrong part / temp range. To test pull one of the leads on the temp. switch and if that lock up the fan, it's time for a new one.

Newbee Note: Power ON to Cadiliac valve solenoid - fan is OFF (everything else correct...)

I don't know if you have this > https://hummerhuren.files.wordpress.com/2013/01/hmmwv_test-diagnostics.pdf < BUT many of these issue are handled with simple reading, easy follow thru and some simple head scratching.


Don't ask, as I don't have much hair left and a multimeter is your friend. CAMO
 

G3isMe

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Thank you for the link to the troubleshooting manual. I did not have that one and have already printed it and completed the troubleshooting outlined in the cooling section. I started the truck and let it idle in the driveway. It only took about 5 minutes before it was over 220 degrees. The fan did not kick on so I unplugged the thermal switch and the fan engaged. I briefly connected the A and B leads and the fan disengaged just as it should according to the manual. Therefore I think it's safe to assume that the fan clutch is operating correctly. So now I have the following:

1) Fan will not engage when engine is hot
2) Fan will engage and disengage when thermal switch is disconnected or bypassed respectively
3) Fan will engage when TDM is disconnected

Does this mean that the thermal switch or TDM is bad or both? I am guessing the thermal switch as it comes before the TDM, correct? I am surprised that it got that hot that fast just idling, but it is 100 frickin degrees out today. I am still planning on doing a antifreeze flush and installing a new thermostat. For the record I have been doing my homework as I do ascribe to the RTFMs before asking for you guru's advice.... :grin:... Thanks in advance for your assistance
G3
 

Retiredwarhorses

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Thank you for the link to the troubleshooting manual. I did not have that one and have already printed it and completed the troubleshooting outlined in the cooling section. I started the truck and let it idle in the driveway. It only took about 5 minutes before it was over 220 degrees. The fan did not kick on so I unplugged the thermal switch and the fan engaged. I briefly connected the A and B leads and the fan disengaged just as it should according to the manual. Therefore I think it's safe to assume that the fan clutch is operating correctly. So now I have the following:

1) Fan will not engage when engine is hot
2) Fan will engage and disengage when thermal switch is disconnected or bypassed respectively
3) Fan will engage when TDM is disconnected

Does this mean that the thermal switch or TDM is bad or both? I am guessing the thermal switch as it comes before the TDM, correct? I am surprised that it got that hot that fast just idling, but it is 100 frickin degrees out today. I am still planning on doing a antifreeze flush and installing a new thermostat. For the record I have been doing my homework as I do ascribe to the RTFMs before asking for you guru's advice.... :grin:... Thanks in advance for your assistance
G3

Start with thermostatic switch...most likely the culprit, won’t open when hot.
 

Milcommoguy

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I note your new to forum? Just got a Hummwv? These cooling issues can be learning experience to new owners and old ones too.

It always a back and forth when trying to "techno guess" issues thru text exchanges.

Based on your deductions, I believe you have narrowed it down. As I said, "multimeter is your friend". MY final test: With the engine Hot at the 230 plus ? degree temperature, shut engine off and measure the switch resistance. At this point it should be and OPEN circuit. Make a good connection and don't burn your pinkies. Only takes a second to check. Add in a couple minutes to find some band-aides for the burn.

As the 4 Star stated, unplug it and drive it. This is all you got and you have to get back to base or pick up supplies (beer) or dodge some bullets. It shouldn't ever get too hot. It should regulate on the mechanical thermostat and that too is a test. (may run a bit cooler) If it runs hot pushing the 240 mark, you have other problems, like clogged up anything, thermostat or a pump. (got water?)

By now you know I like my...

VOM.jpg

MULTIMETER, VOM, DVM, etc.

Takes the guessing out of many electrical problems. With a clear understanding of this cooling system, you will be able to leave it home. Then it will be something else, so mine lives in the truck.

Don't buy cheap parts. Get the REAL DEAL, or you'll be right back here.

OH... By the way, you probably have never heard the roar kick in? Get ready for it! And and and it should roar with it un-plugged. It's the leaf blower effect all the time.

Now where did I put that meter thingie? CAMO
 
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McSpeed

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This is a great thread. When I got my truck, the caddy valve was bad so the fan ran all the time. It stayed a cool 180 but DANG...it has ZERO power. Thanks to SS I found out how to test it - narrowed it down...and I replaced that, and saw that when the gauge showed around 220 to 230, the fan would kick in. Sounds like a bomb going off the first time it happens on the time delay. Scares the crap out of you...then you are like "oh...that's just the fan." My gauge was fluttering bad, so I bought a new gauge and sender unit. - around this same time my glow plug light wasn't working. The TSU was bad so I replaced it and the gauge/sender. Glow plugs work correct now. But, now (per the gauge), it runs right at 230 ish...(per the gauge) and the fan kicks on and off fairly frequently. The fan kicks on for a short time...and back off. I thought it was supposed to run it down much cooler then cycle off - but mine cycles off pretty quickly and moves it down just enough to be under the trigger point. I've replaced the water pump, t-stat, and flushed out the cooling system last year. I've yet to get my laser gauge on it - seems like when I remember it is doing this...I'm already down the road without my scanner. Not sure where I want to scan it with the laser to confirm the right temp.

There is NO steam, no boil, and no overflow of coolant. So...I "assume" she is just fine, and for some reason likes to run right on the edge. Doesn't matter if it is a hot summer day or cold day, there is a path I drive out to a state park - the fan kicks on in almost the exact same spot for the first time from my house. About four miles.

So I think maybe...the time delay or something isn't staying engaged long enough for some reason and I think the gauge seems to read a bit on the hot side. But, no steam...no boil...doesn't smell excessive hot. So, maybe okay.
 
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